Industrial Wireless Sensor Networks (IWSNs) are found in many application domains that require low latency, robustness, and determinism. The IEEE 802.15.4 standard is not able to cope with the requirements of these applications. For this reason, the IEEE 802.15.4e amendment was introduced, which provides novel MAC-layer profiles that are optimized for a broad range of application domains, including process automation. This paper focuses on two of these profiles, i.e., the Deterministic and Synchronous Multi-channel Extension (DSME) and the Time Slotted Channel Hopping (TSCH). The aim of the paper is twofold. First, assessing their behavior in realistic process automation scenarios. Second, comparing their performance in terms of end-to-end delay, reliability and scalability. The ultimate aim of the work is identifying the limits of those protocols, thus paving the way to further work addressing suitable approaches to tackle them.